1. Field of the Invention
The present disclosure relates to a light source apparatus for emitting beams of light of a plurality of wavelengths, and relates to a method of controlling a light source apparatus.
2. Description of the Related Art
Light source apparatuses for emitting light of a stabilized wavelength are developed for use in a light source of a length measuring device using interference, and in alight source for the frequency calibration (an optical frequency standard) of a semiconductor laser for optical communication. Generally, a light source apparatus having a stabilized wavelength includes a light source to be stabilized, a wavelength discriminator (a wavelength reference device) that converts a change in wavelength of the light source into a change in light intensity, and a detector that converts the light intensity into an electric signal. The light source apparatus further includes a calculator that obtains a wavelength error based on the electric signal from the detector, and a control unit that controls the light source based on the wavelength error.
As a light source apparatus for use in a light source of a length measuring device, an interferometer, and optical communication, a light source apparatus is known that stabilizes beams of light of a plurality of wavelengths and simultaneously outputs the beams of light. To stabilize beams of light of a plurality of wavelengths, as in a light source apparatus described in Japanese Patent No. 2712965, a method is known of stabilizing beams of light of a plurality of wavelengths with respect to each wavelength, and thereafter multiplexing the beams of light.
The light source apparatus of Japanese Patent No. 2712965 uses a Fabry-Perot cavity (an etalon) and a wavelength tunable laser as a wavelength discriminator. The light source apparatus multiplexes laser light from the wavelength tunable laser having a wavelength stabilized in advance to a first transmission peak of the etalon, with beams of light from light sources of a plurality of wavelengths, and detects a beat signal between the beam of light of a first wavelength among the plurality of wavelengths and the laser light from the wavelength tunable laser, thereby stabilizing the first wavelength of the light source apparatus based on the beat signal.
Next, the light source apparatus stabilizes the wavelength of the laser light from the wavelength tunable laser to a second transmission peak of the etalon, thereby similarly stabilizing a second wavelength of the light source apparatus. The light source apparatus performs this process on the beams of light of all the wavelengths, and thereby can stabilize the wavelengths of the light sources.
The light source apparatus of Japanese Patent No. 2712965, however, cannot simultaneously stabilize a plurality of different wavelengths. Consequently, an increase in the number of wavelengths of light sources to be stabilized increases the time during which each wavelength is not controlled. This reduces the accuracy of the stabilization.
In response, as in a light source apparatus described in Japanese Patent Publication No. 04-082194, a method is known of using a plurality of wavelength stabilizing apparatuses, the apparatuses including a wavelength discriminator and a calculator that are made common.
The light source apparatus of Japanese Patent Publication No. 04-082194 uses two light sources that emit linearly-polarized beams of light orthogonal to each other, coaxially multiplexes the beams of light from the respective light sources to guide the multiplexed beams of light to a wavelength discriminator (an etalon or a gas cell), and splits the beams of light by a polarizing beam splitter to detect the light intensity of each light source by a photodetector.
The light source apparatus of Japanese Patent Publication No. 04-082194, however, uses the polarizing beam splitter to separate the multiplexed beams of light of a plurality of wavelengths. Thus, even the use of a polarizing beam splitter having a high extinction ratio results in mixing the separated beam of light of one of the wavelengths with the separated beam of light of the other wavelength. Consequently, in one of the stabilization control systems, the other beam of light is mixed. This reduces the accuracy of the stabilization of wavelengths.